High efficiency, high power density and high reliability have always been the industry's requirements for power converters. High efficiency means reduced energy consumption, which is advantageous in energy conservation and emissions reduction, protecting the environment, and reducing cost of usage. High power density stands for small volume and light weight, which reduces cost in material, cost in transportation and space requirements, so as to reduce cost in construction. High reliability means longer service life and lower cost in maintenance.
A semiconductor device is one of key factors for efficiency of the power converter. During application, some auxiliary parts are inevitable, e.g., clamps and screws for fastening the semiconductor device, thermal pads for facilitating heat dissipation. Since discrete devices are large in number, it is tedious to install these auxiliary parts. Besides, due to the purpose of standardization for the discrete devices, utilization ratio of internal spaces is extremely low. For a typical TO-247 package in FIG. 1A-FIG. 1C as a standard discrete device package, it includes a plastic package material 10, heat dissipating sheet 20 covering the plastic package material 10, pins 40 electrically connected a chip 30 packaged in the plastic package material 10. As a result, the chip 30 occupies a principal plane (X-Y) of the plastic package material 10 by a ratio which is generally less than 40%. Integrated Power Module gradually advents to meet an increasing demand for improved performance of a power supply. A basic idea of such demand is to integrate a plurality of power semiconductor devices (usually in a form of bare chips) with small area into a module, so as to be possible to implement a high utilization ratio of space.
Reference is made to FIG. 2, it is a schematic view of a smart power module in the prior art. As shown in FIG. 2, the smart power module includes power devices 50, magnetic components 60 (e.g., a transformer, an inductor or the like), a control device 70, and passive components 80 (e.g., a resistor, a capacitor or the like), which are soldered on a substrate 90 together and form functional circuit connections and connect with an external system board by in-line pins 40.
To further improve heat dissipation capability and reliability of a high power module, a high-thermal conductive plastic package material is used in the industry to encapsulate all of the components into a block, so that heat can be conducted to a radiator 100 on the module through the plastic package material and thus be dissipated. The pins 40 can be electrically and mechanically connected with a side wall of the substrate 90 (shown in FIG. 3A and FIG. 3B). The pins 40 can also be soldered to a surface of the substrate 90 by means of a lead frame, and then led to outside by means of bending (shown in FIG. 4).
Structures of the power module described above have relatively high integration degree and power density. However, they suffer from a drawback that they occupy a large area of the external system board. In order to further reduce the occupied area of the power module, the power module can be divided into several parts such as two parts and the several parts are stacked with each other to form a module with vertically stacked structure. FIG. 5 is a schematic view of vertically stacked power modules in the art. As shown in FIG. 5, in a typical structure, the power device 50 and the magnetic components 60 are set on an upper substrate 901, while the control device 70 and some of the passive components 80 are soldered to a lower substrate 902. And the lower substrate 902 is vertically connected with the upper substrate 901 by an upper pin 401, and the lower substrate 902 is vertically connected with a system board by a lower pin 402. Though the method of connection implements stacked structures of the power modules in a vertical direction and reduces the occupied area, it still has the following drawbacks:
1) The process for producing pins and inserting pins into the substrate has a low efficiency and a high cost.
2) Pin connections between the upper and lower substrates occupy additional area on the substrate.
3) It is difficult to make a plastic package of the structure as a whole and to dissipate heat from the structure, and the structure has a poor structural reliability.